ISOZYME VARIATION AND SPECIES DELIMITATION AMONG DIPLOID POPULATIONS OF THE PUCCINELLIA-NUTTALLIANA COMPLEX (POACEAE) - CHARACTER FIXATION AND THE DISCOVERY OF PHYLOGENETIC SPECIES

Phylogenetic species, the minimal elements appropriate as terminals in phylogenetic analysis, are population systems that are differentiated by unique (i.e., diagnostic) character combinations. Within the predo minantly polyploid Puccinellia nuttalliana species complex, two diploi d taxonomic species are recognized on the basis of morphology. Isozyme variation was analysed in 11 diploid populations identified as P. lem monii and one identified as the rare P. parishii, and variation profil es were generated for each population, reflecting each allele as eithe r absent, present and fixed, or present and not fixed. Population Aggr egation Analysis (PAA) grouped these populations into two distinct iso zyme species that correspond precisely in membership to the species re cognized previously on the basis of morphology; thus, isozyme patterns are congruent with those of morphology. Mean genetic identities among populations of P. lemmonii are not unusually high for conspecific pla nt populations, nor are genetic identities between populations of the two species unusually low.